Field of the Invention
The present invention relates to an optical displacement sensor equipped with an imager having an automatic exposure stopping function of automatically stopping the exposure of a pixel receiving the light.
Description of Related Art
The automatic exposure function currently implemented in the conventional imaging device is so designed as to set the exposure time for the subsequent shooting by performing such a calculation as that of the average brightness of the entire pixels or the average brightness of specific pixels through processing of an image that has been shot and depending on difference between the calculation result and a target value.
FIG. 13 of the accompanying drawings illustrates a structural diagram showing the automatic exposure function implemented in the conventional imaging device and FIG. 14 thereof illustrates a time chart showing the operation of the automatic exposure function shown in FIG. 13. Referring to FIG. 13, in response to the light reflecting from a target or an object M and subsequently received by a pixel, the light is received by a group of pixels for a constant exposure time and, subsequent to read-out from a pixel read-out unit 52, the average brightness is calculated by an average brightness calculation unit 53. The average brightness so calculated and a target value of a target average brightness unit 55 are compared with each other by a comparator 54 so that the exposure time is set by a subsequent exposure time setting unit 56. If the average brightness is lower than expected, the exposure time is set to longer time and the average brightness is higher than expected, the exposure time is set to shorter time. Instead of the average brightness, the peak brightness is occasionally used. As shown in FIG. 14, exposure 61 • pixel read-out 62 and the average brightness calculation 63 are executed, comparison 64 and exposure time setting 65 are executed and, under a new exposure time, the exposure 61 • the exposure element read out 62, the average brightness calculation 63, the comparison 64 and the exposure time setting 65 are repeated. As discussed above, since the conventional automatic exposure function includes read-out of the pixel (image) that has been exposed (shot) and the subsequent exposure time is set after the calculation process, problems have been recognized that the exposure time is unable to follow perfectly in the event that the light reflecting level of the object changes dynamically, and the image temporarily underexposed or overexposed is unusable.
In order to improve those problems, the patent document 1 listed below, for example, discloses an imager of a kind having an automatic exposure stopping function with which exposure or light emitting is stopped when a peak value of the light receiving level is detected. With this known imager, since the exposure is stopped at the moment the light receiving level reaches a specified level, such a problem with a less light receiving level or saturation can be avoided.